1. Field of the Invention
The present invention relates to Composition for thermister, in particular such composition for NTC (Negative Temperature Coefficient) thermister for temperature detection, and to composition for realizing a highly reliable thermister where B constant thereof is 2000 to 3000K and resistance values changing with time passing are small.
2. Description of the Related Art
As a conventional NTC thermister for temperature detection, there are known compositions containing manganese, cobalt and nickel for the thermister comprising oxide semiconductor of main manganese oxide.
For making small changing ratio with time passing of resistance values of the thermister composition consisting of manganese, cobalt and nickel as main components used at high temperature and high moisture, it has been proposed to add one kind or more of ZrO.sub.2 or CuO at determined contents (for example, Unexamined Japanese Patent Publication (kokai) No. 6-231905).
However, in the thermister composition comprising oxides of two kinds of metallic elements of manganese and nickel, or in the thermister composition where ZrO.sub.2 or CuO were added to these oxides, the B constant was large as 3000K or more, and it was difficult to apply for compensating temperature of TCXO (quartz oscillator of temperature compensation type).
Incidentally, for the quartz oscillator of temperature compensation type, two thermisters are ordinarily used for low temperature side (-30 to 25.degree. C.) and for high temperature side (25 to +85.degree. C.).
However, in view of using environment of recent machinery, for minimizing changes in the oscillator due to temperature even in the low temperature side, there is a problem that unless the B constant of the thermister falls within a specific range, the temperature compensation of the quartz oscillator is not sufficient.
It is said that the B constant of the thermister is very preferable in "2000 to 3000K".
There is still a further problem that the resistance changing ratio at the high temperature and high moisture is large.